Berichtzusammenfassung

High resolution seismic seabed imaging

The motivation for this research project was the many inquiries from different branches of industry to geophysical companies, for imaging and/or mapping methods able to detect isolated objects buried in the seabed sediments, or very localised discontinuities in the geological structure.

The project has therefore investigated the feasibility of scrutinising the first 15 metres under the seafloor, with a metric resolution (up to 0.5 m). Such resolution would enable to: check planned pipeline routes; avoid problems in connection with drilling, skirt penetration, conductor installation and land piling, etc.

The main results of the project are: development of a full-scale test facility for testing innovative geophysical procedures (the facility, which includes three targets buried at different depths, was used in the course of the project, but may be useful also for subsequent research work); application of very high resolution seismic survey techniques (the use of different sources was explored and new types of seismic sources were developed); development of new techniques for numerical modelling and imaging; feasibility studies of a new type of sonar, based on Stoneley-Scholte waves, explored by reduced-scale tank experiments (appropriate instrumentation was developed (a marine vibrator and a set of receivers) and tested in the full-scale site test and the excitation, the recording and the processing of surface acoustic waves proved feasible); publications related to the work development; final processed seismic data (ie 2D stacks and 3D stacked data).

The desired metric resolution turned out to be very difficult to achieve, if at all possible with the current state of the art. A number of further improvements, aimed at increasing the resolution actually achieved in the course of the project, have been identified and recommended for future research work. The project is more extensively described in project final reports and in the web page http://www.ismes.it/seabed.